Abstract. The published data on the preparation and theThe published data on the preparation and the
dispersion-structural properties of nano-sized TiOdispersion-structural properties of nano-sized TiO22 areare
considered. Attention is focused on its sol ± gel synthesisconsidered. Attention is focused on its sol ± gel synthesis
from different precursors. The possibilities for the purpose-from different precursors. The possibilities for the purpose-
ful control and stabilization of properties of TiOful control and stabilization of properties of TiO22 nano-nano-
powders and sols are analyzed. Information onpowders and sols are analyzed. Information on
physicochemical methods used in studies of the particlephysicochemical methods used in studies of the particle
size and the phase composition of nanodisperse TiOsize and the phase composition of nanodisperse TiO22 isis
presented. The prospects of using nano-sized TiOpresented. The prospects of using nano-sized TiO22 inin
medicine and nanobiotechnology are considered. The bib-medicine and nanobiotechnology are considered. The bib-
liography includes 95 referencesliography includes 95 references..
I. Introduction
Due to its unique properties, nano-sized titanium dioxide
represents a promising research subject for various modern
fields of science and technology, including microbiology,
nanobiotechnology and fundamental medicine. Thus the
most popular directions include the design of a new gen-
eration of drugs based on synthetic nanobioconstructs
containing TiO2 nanoparticles and aimed at curing cancer
and viral or genetic diseases. The necessity of developing
new approaches to fight against these diseases is associated
with the limitations inherent in conventional methods of
therapy and profilaxis. Thus for viral infections, the therapy
efficacy tends to decrease due to permanent mutation of
viruses.
Development of methods for the targeted impact on
injured RNA and DNA molecules includes studies of the
conjugates of oligonucleotides containing biologically
active or photoreactive ligands targeted to a certain frag-
ment of a nucleic acid.1 ± 3 Numerous oligonucleotides and
their derivatives capable of an in vitro selective effect on
nucleic acids were synthesized. The main problem of these
studies was associated with the absence of reliable and
efficient methods for the drug delivery to cells, because
viruses are localized inside a cell and oligonucleotides fail to
effectively penetrate there due to their high molecular
weight and the hydrophobic nature of cell membranes. To
solution of this problem, the methods of nanotechnology
and nanobiotechnology oriented at employing nanopar-
ticles as drug-loaded `nanovectors' are engaged.4 Thus
oligonucleotides were immobilized on TiO2 nanoparticles.5
Covalently linked TiO2 ±DNA nanocomposites were shown
to possess the unique property of a light-inducible nucleic
acid endonuclease.6
The first publication 7 on the use of titanium dioxide in
microbiology for photoelectrochemical sterilization of
microbial cells dates back to 1985; since that time, the
number of studies devoted to the bactericidal effect of
nanodisperse TiO2 with respect to different pathogenic
bacteria is being permanently increased.8 ± 17 Data on the
efficient blood purification from residual viruses by filtering
it through nanoceramic membranes or nanofibres contain-
ing nanostructured TiO2 are documented.18
Recently, publications have appeared devoted to studies
on the possibility of using TiO2 in oncology.19 ± 22 This is
associated with the quest for an alternative to two main
methods of treating malignant tumours, i.e., radio- and
chemotherapy. For example, it was demonstrated 22 that the
growth of the Ls-174-t culture of human colon carcinoma
Z R Ismagilov, L T Tsykoza, N V ShikinaGK Boreskov Institute of
Catalysis, Siberian Branch of the Russian Academy of Sciences,
prosp. Akad. Lavrentieva 5, 630090 Novosibirsk, Russian Federation.
Fax/tel. (7-383) 330 62 19, e-mail: [email protected] (Z R Ismagilov),
tel. (7-383) 326 95 38, e-mail: [email protected] (L T Tsykoza),
tel. (7-383) 330 76 70, e-mail: [email protected] (N V Shikina)
V F Zarytova Institute of Chemical Biology and Fundamental Medicine,
Siberian Branch of the Russian Academy of Sciences, prosp. Akad.
Lavrentieva 8, 630090 Novosibirsk, Russian Federation.
Fax (7-383) 333 36 77, tel. (7-383) 335 62 24,
e-mail: [email protected]
V V Zinoviev State Research Centre of Virology and Biotechnology
`Vector', 630559 Koltsovo, Novosibirsk Region, Russian Federation.
Fax (7-383) 336 74 09
S N ZagrebelnyiNovosibirsk State University, ul. Pirogova 2,
630090 Novosibirsk, Russian Federation. Fax (7-383) 330 22 42,
tel. (7-383) 363 42 59, e-mail: [email protected]
Received 28 May 2009
Uspekhi Khimii 78 (9) 942 ± 955 (2009); translated by T Ya Safonova
DOI 10.1070/RC2009v078n09ABEH004082
Synthesis and stabilization of nano-sized titanium dioxide
Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
Contents
I. Introduction
II. The effect of synthesis conditions on the degree of dispersion, phase composition and properties of titanium dioxide
III. Synthesis of nano-sized TiO2 from titanium alkoxides; product dispersion and phase composition
IV. Synthesis of nano-sized TiO2 from TiCl4 ; product dispersion and phase composition
V. Synthesis of TiO2 from miscellaneous titanium-containing precursors
VI. Stabilization of the disperse state and phase composition of nano-sized TiO2 sols
Service code 4082
Last printed
28 october 11:28:32
Russian Chemical Reviews 78 (9) ? ± ? (2009) # 2009 Russian Academy of Sciences and Turpion Ltd
cells can be suppressed by treating these cells with a dilute
TiO2 colloid solution followed by irradiation. The tumour
cells were effectively killed in vitro by photoexcited TiO2
nanoparticles. The survival ratio after 30-min irradiation
decreased rapidly with the increase in TiO2 concentration.
In Russia, studies devoted to the development of syn-
thetic nanoconstructs involving TiO2 particles for the tar-
geted genome cleavage are of the innovating nature and
largely represented by proceeding of conferences.23 ± 27 It
was demonstrated 27 that nanocomposites built of titanium
dioxide nanoparticles with immobilized polyamine-contain-
ing oligonucleotides interact with 30-mer [32P]RNA and
[32P]DNA targets. It was shown that UV irradiation of
complexes formed results in modification of the targets.
Nanocomposites based on complexes of amorphous TiO2 ±
polylysine nanoparticles with oligonucleotides exhibited
antiviral activity, which was especially pronounced under
UV radiation carried out 2 ± 3 h after infection. Obviously,
the prerequisite for the use of TiO2 in such constructs was
its nanoscale size and colloidal state, which ensured the
efficient penetration of nanostructures into cells.
The low cytotoxicity of TiO2 nanoparticles was
noted,25, 26 which, however, differed for different cell cul-
tures and depended on the titanium dioxide phase compo-
sition. The low toxicity of TiO2 nanoparticles was also
demonstrated in another study 28 where a well-known in
vitro procedure was used that assesses the organism
response to dust from the induction of proinflammatory
cytokines IL-6 and IL-8 generated by respiratory tract
epithelium cells treated with relevant particles. It was
shown that nanoparticles of commercial metal oxides
including TiO2 are not too toxic with respect to lung cells
as compared with the environmental dust particles. It also
followed from the results of this study that contrary to
expectations, the metal oxide nanoparticles were not more
toxic than micron-sized particles.
Nano-sized titanium dioxide finds wide application in
other modern scientific and technological fields including
photocatalysis, electrochemistry, optics, microelectronics,
in the production of dyes, ceramics, cosmetics, gas sensors,
inorganic membranes, dielectrics, in the synthesis of meso-
porous film coatings, catalysts for environmental cleaning
processes, etc.29 ± 44
Thus, the synthesis and stabilization of nanodisperse
forms of TiO2 is a challenge for science and practice.
The most popular method of synthesis of disperse
deposits of metal oxides including TiO2 is their precipita-
tion from the solutions of the corresponding salts with
ammonia, alkalis and alkali-metal carbonates. Numerous
studies have shown that the minimum size of primary
particles is independent of the nature of the precipitating
agent being equal to 45� 10 �A.45 Depending on the syn-
thesis conditions, the primary particles coalesce to form
different-sized aggregates. The degree of aggregation
depended on many factors and was controlled by the syn-
thesis conditions. Varying the temperature, the synthesis
time and pH of the medium allowed fabrication of titanium
dioxide with different phase compositions, namely, amor-
phous TiO2, anatase, brookite or rutile.
The present review summarizes studies on the synthesis
of nano-sized titanium dioxide and the control and stabili-
zation of the dispersed state, morphology and phase com-
position of TiO2 nanoparticles and also discusses the
prospects of their use in nanobiotechnology.
II. The effect of the synthesis conditionson the degree of dispersion, phase compositionand properties of titanium dioxide
According to early studies,45 hydrolysis of different tita-
nium compounds (titanium alkoxides and inorganic salts,
mainly, TiCl4) in aqueous solutions with low pH (2 ± 6)
resulted in basic salts with variable compositions as the
primary products. At higher pH, titanium dioxide hydrates,
presumably, with the composition TiO(OH)2 or
TiO2. nH2O, where n depends on the ageing and drying
conditions, form.
Freshly precipitated titatium(IV) dioxide hydrate exhib-
ited high adsorbability with respect to both cations and
anions; the content and the nature of impurities in TiO2
depended on the pH of the medium and the nature of both
the precipitating agent and the starting titanium com-
pound.45 According to the data from transmission electron
microscopy (TEM), the TiO2 gel represented spherical non-
porous particles with the sizes 30 ± 60 �A aggregated into
chains and bunches. The gel specific surface (S ) varied from
250 to 500 m2 g71 (Refs 45 and 46) and depended on the
precipitation conditions and the presence of impurities
(Fig. 1, 2).45
5 10 pH
300
400
Sm2 g71
1
2
Figure 1. Dependence of the specific surface of titanium dioxide
hydrate on the pH of the medium in the course of sedimentation at
room temperature (1 ) and 70 8C (2).45
1
2
25
30
logS (m2 g71)
0 0.05 0.10
Cl content /mequiv g71
Figure 2. Dependence of the specific surface of titanium dioxide
hydrate on the chloride ion content.45
(1 ) Sedimentation at room temperature, (2) at 70 8C.
2 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
The specific surface of titanium dioxide hydrate formed
upon hydrolysis under hydrothermal conditions also
depended substantially on the temperature and the duration
of the process.47 Strong effect of the initial concentration of
TiCl4 , which determines the reaction medium acidity, on
the degree of crystallinity of the hydrothermal hydrolysis
product was obseved.48
A simple and accessible method of synthesizing pure and
stable nano-sized TiO2 (anatase) under mild hydrothermal
conditions using TiCl4 as the precursor was proposed.49
Solvothermal hydrolysis of titanium ethoxide in anhydrous
ethanol containing strictly definite amount of ultrapure
water, carried out under mild conditions (<200 8C, 2 h),
also afforded pure ultradisperse nanocrystalline anatase
with high specific surface (up to 250 m2 g71).50
Thermal treatment of gels of different titanium dioxide
hydrates resulted in their crystallization to form anhydrous
TiO2 . Depending on the calcination temperature, hydrated
TiO2 could be transformed into anatase, rutile or brookite,
which was accompanied by changes in its specific surface
and porous structure. Thus at temperatures below 600 8C,crystallization produced anatase with the virtually constant
pore volume and specific surface.51 For higher temper-
atures, the transition of anatase to rutile occurred with
concomitant sharp decrease in both the pore volume and the
specific surface (Fig. 3). Mineral impurities could also exert
a strong effect on the polymorphous transition temperature.
Numerous data have shown that besides the phase compo-
sition, the conditions of thermal treatment of TiO2 gels
determined other important performance characteristics of
titanium dioxide, namely, its morphology and the particle
size.
The production of TiO2 is carried out, most often, by the
sulfate and chloride methods (from ilmenite and TiCl4,
respectively). Titanium tetrachloride can be processed
according to three different schemes, namely, hydrothermal
hydrolysis, vapour-phase hydrolysis and combustion in an
oxygen flow. Recently, the sol ± gel method that affords
TiO2 particles with desired structures and properties has
gained in importance and, hence, has attracted attention
from the viewpoint of development of nanotechnologies.
Titanium alkoxides or titanium tetrachloride were used as
the titanium-containing precursors in the sol ± gel method.
In the following sections, the most significant results in
the control over dispersion, morphology, phase composi-
tion and stability of nano-sized TiO2 are considered.
III. Synthesis of nano-sized TiO2 basedon titanium alkoxides; product dispersionand phase composition
In the synthesis of TiO2 from alkoxides, titanium tetraiso-
propoxide (from hereon, isopropoxide) and titanium tetra-
butoxide (butoxide) are preferred.
Colloid solutions of TiO2 with different particle sizes
and stability were synthesized 52 from acetylacetone-modi-
fied Ti(OPri)4 using organic solvents that differed in polar-
ity and molar volume. According to data from X-ray phase
analysis, irrespective of the nature of organic solvents used
in the hydrolysis, all freshly prepared sols obtained both
with or without acetylacetone contained amorphous TiO2
that was transformed into the nanocrystalline anatase phase
when heated to 450 8C. However, the use of solvents with
small molar volumes and modification of the precursor with
acetylacetone resulted in stabilization of the TiO2 colloid
solution, which actually was the principal result of the study
cited above. An IR spectroscopic investigation suggested
the formation of a chelate complex of titanium isoprop-
oxide with acetylacetone (Fig. 4), which presumably slowed
down the hydrolysis and condensation and, hence,
decreased the degree of agglomeration of TiO2 particles;
the effect of solvent on the aggregate size (Fig. 5) was
rationalized in terms of the Hansen solubility parameters.
The Hansen solubility parameters found for TiO2 samples
prepared in different solvents in the presence of acetylace-
tone may be useful in the synthesis of stable colloidal TiO2 .
The data of the size of TiO2 particles in colloid solutions
and the degree of their aggregation in dry powders were
obtained using light scattering, scanning electron micro-
scopy (SEM) and TEM.52
Titanium isopropoxide, diethanolamine (DEA) and
ethanol (3 : 1 : 20 by volume) were used 53 as the starting
reagents in the fabrication of TiO2 sols. The mixing order
played an important role. Thus the introduction of EtOH
before DEA led to very fast sedimentation of TiO2 due to
the high reactivity of the alkoxide in ethanol. Hence, first,
half volume of ethanol was mixed with DEA and then
titanium isopropoxide was added; the mixture was stirred
for 30 min and the remaining amount of EtOH was added.
The resulting mixture was vigorously stirred at room
temperature. The obtained sol was stable for a week and
then transformed into gel. A considerable increase in sol
stability was observed with a decrease in its stirring time.
0.4
0.8
400 800 T /8C
Pore
volume/cm
3g7
1
a
71
0
1
2
log S (m2 g71)
400 800 T /8C
b
Figure 3. Changes in the porous structure (a) and the specific surface
(b) of titanium dioxide in the calcination.51
Synthesis and stabilization of nano-sized titanium dioxide 3
The sol stability also substantially increased under low
humidity conditions. In the course of drying, the formation
of a xerogel considerably `shrinked' as compared with the
starting gel was observed, the volume decreased five- to
tenfold.
A pure anatase phase with particle sizes of 10 ± 20 nm
was prepared 54 by a very simple low-temperature (100 8C)procedure using only water as the medium and titanium
isopropoxide as the precursor (without additives). The size,
shape and phase composition of particles were studied by
X-ray phase analysis and TEM.
Nanoparticles of TiO2 obtained by hydrolysis of
Ti(OPri)4 at various pH were studied.55 For the subsequent
preparation of nanopowders with narrow size distribution,
the final suspension was peptized. The effect of pH on the
size and morphology of particles in nanopowders was
evaluated. According to XRD, SEM and TEM data, the
as-prepared powders entirely consisted of the anatase crys-
talline phase. Only the powder prepared in a strongly acidic
solution contained fine spherical particles. It was shown
that the anatase to rutile transformation occurred at tem-
peratures below 600 8C.In a different study,56 the preparation of colloidal
titania with the concentration of 0.9 mol litre71 involved
hydrolysis of titanium isopropoxide in a mixture of iso-
propyl alcohol with 2 M hydrochloric acid.
In yet another study,57 the synthesis of nanostructural
films involved the preparation of a TiO2 sol by hydrolysis of
titanium isopropoxide in a mixture of ethanol with hydro-
chloric acid (molar ratio Ti(OPri)4 : HCl : EtOH :H2O=
1 : 1.1 : 10 : 10), which was followed by the addition of an
a
b
c
e
d
f
g
4000 3000 2000 �n /cm71
Transmission
1
3
3
3
3
3
3
2
Figure 4. IR spectra of acetylacetone (a) and titanium dioxide sols
prepared in the presence of acetylacetone in different organic solvents:
THF (b), acetone (c), butanol (d ), chloroform (e), toluene ( f ),
hexane (g).52
(1 ) Peak of the C=O group of the keto form, (2) peak of the C=O
group of the enol form, (3) peak of the C=O group of the chelate
complex.
a
c
e f
b
d
10 nm
3 mm15 mm
Figure 5. SEM microimages of titanium dioxide sols synthesized in
the presence of acetylacetone in acetone (a), butanol (b), toluene (c, e)
and hexane (d, f ).52
Images (e) and ( f ) were obtained at larger magnification.
4 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
aqueous methylcellulose (MC) solution. It was shown that
an increase in the water content and the sol dilution retards
gelation.
Calcination of a titanium dioxide sol afforded TiO2
nanopowder to be used in the preparation of homogeneous
suspensions for the purpose of producing films. The stabil-
ity of TiO2 suspensions was investigaed 57 by measuring the
sedimentation rate. The anatase powder concentration in
liquid was varied (5 mass%± 10 mass%) in the presence
and in the absence of MC. It was shown that the sedimen-
tation rate of the TiO2 nanopowder sharply decreased in the
presence of MC. For example, in 5% and 10% suspensions
containing no MC, the sedimentation took 1 h and 30 min,
respectively, whereas, in the presence of MC the 5%
suspension remained stable for 3 days and the beginning
of the settlement in 10% suspension began after 10 h. Thus,
MC served as the dispersant. The SEM data pointed to a
considerable increase in homogeneity and uniformity of
TiO2 films and their higher specific surface in the presence
of MC (Fig. 6).
The synthesis of nano-sized TiO2 by the sol ± gel method
on the basis of titanium isopropoxide was carried out in the
presence of a peptide, poly-L-lysine (PLL), as an additive.58
In this case, peptide served not only as the dispersant but
also as the structure-determining additive: it was only in the
presence of PLL that tubular TiO2 particles were formed
(Fig. 7 a). The particles retained their shape after calcina-
tion at 700 8C (Fig. 7 b). For a sample obtained in the
absence of PLL, calcination at the same temperature led to
titanium dioxide with irregular structure (Fig. 8). Accord-
ing to XRD data, titanium dioxide obtained in the presence
of PLL and calcined at 700 8C represented anatase with a
rutile admixture. In TEM microimages, nanoparticles with
the anatase diffraction pattern looked as either coupled
tubes with the diameter of 20 nm and the Y-shaped junction
in the lower part or nanorods with the diameter from 10 to
25 nm. Materials based on nano-sized TiO2 with the tubular
structure can successfully be used in medicine, biotechnol-
ogy, microelectronics, optics, etc.58
5 mm
a
b
5 mm
Figure 6. SEM microimages of TiO2 films after thermal treatment
at 500 8C of samples with addition of (a) and without methylcellulo-
se (b).57
500 nm
1 mm
a
b
Figure 7. SEM microimages of TiO2 syntheized in the presence of
poly-L-lysine.58
(a) As-prepared sample, (b) sample after calcination at 700 8C.
1 mm
Figure 8. SEM microimage of a TiO2 sample prepared without poly-
L-lysine after calcination at 700 8C.58
Synthesis and stabilization of nano-sized titanium dioxide 5
Nano-sized mixed colloids with the composition PAA±
TiO2 [PAA is poly(acrylic acid)] were synthesized 59 by an
in situ sol ± gel method using titanium isopropoxide and a
PAA solution in butanol. Depending on whether tutanium
isopropoxide was added before or after the complete dis-
solution of PAA, the solid phase separation and gelation
scenarios differed; however, after heating, stable colloidal
solutions were formed in both cases. To confirm the
presence of interactions between PAA and Ti, the PAA : iso-
propoxide : water molar ratio was varied. The formation of
chelate complexes was reliably confirmed by IR spectro-
scopy. Differential scanning calorimetry (DSC) also dem-
onstrated strong interaction between PAA and Ti, which
confined the motion of PAA chains. Moreover, according
to the data from thermogravimetric analysis (TGA), the
thermal stability of PAA chelate was higher as compared
with the free acid. On the whole, as followed from TEM
results, the order in which reagents were mixed and the
PAA : isopropoxide : water molar ratio substantially
affected the size and the shape of PAA ±TiO2 hybrid
aggregates and the degree of aggregation.59
Nanocrystalline TiO2 was deposited from an ethanolic
solution of titanium isopropoxide and hydrogen peroxide
by refluxing at 80 8C for 2 days.60 The resulting particles
were filtered and dried at 100 8C. Elucidation of the role of
subsequent treatment on the physicochemical and electro-
chemical properties of nanocrystalline TiO2 was carried out
using XRD and TEM of as-prepared powder, a sample
calcined at 400 8C and a sample following sonication.
According to the data from X-ray diffraction analysis, all
samples represented the anatase phase. The TEM studies
have shown that the dried sample consisted of uniform
spherical particles measuring 5 nm. In the sample calcined
at 400 8C, the particles retained their spherical shape but
their size increased to 10 nm. The sample subjected to
sonication for 5 h contained a considerable fraction of
particles with the average diameter of 5 nm and the length
of 20 nm.
Mesoporous titanium dioxide with bimodal pore size
distribution was prepared 61 by sonication-assisted hydrol-
ysis of titanium isopropoxide in EtOH : water with the
molar ratio equal to 1:1 (sample R1) and 10:1 (sample
R10) and also in pure water (sample R0). According to
data from XRD, nanostructured xerogels formed after
drying the hydrolysis products of R0, R1 and R10 at
100 8C represented an anatase and brookite mixture, pure
anatase and the amorphous TiO2 phase, respectively.
With the increase in calcination temperature, substantial
changes in the qualitative and quantitative composition of
the samples studied were observed (Fig. 9). Thus in R0
sample, the rutile phase appeared as soon as at 600 8C when
the brookite phase was still present in a noticeable amount;
at 700 8C, virtually all anatase was transformed to rutile. In
R1 sample, small amount of brookite appeared at 400 8Cbut disappeared at 600 8C. This was accompanied by an
increase in the anatase fraction, but the rutile admixture
also appeared. At 700 8C, approximately half amount of
anatase transformed to rutile. For amorphous xerogel R10,
anatase nanocrystals appeared only at *373 8C and under-
went no phase transitions up to 600 8C. Only at 700 8C, thetransformation of anatase to rutile started.
Figure 10 shows that phase transitions in samples R0,
R1 and R10 were accompanied by the increase in the size of
TiO2 particles, which was more pronounced at temper-
atures above 500 8C being associated with the rutile for-
mation. All TiO2 powders calcined at 400 ± 600 8C were
characterized by bimodal pore size distributions with max-
imum pore diameters at 2 ± 4 and 16 ± 24 nm. At 700 8C, allsamples demonstrated monomodal pore size distribution as
the result of destruction of fine pores.
Pyrolysis of homogeneous TiO2 gels prepared by
hydrolysis of titanium isopropoxide pretreated with for-
mic 62 or oxalic 63 acids with the aim of controlling the
gelation process was studied. The amorphous titanium
dioxide gel was characterized by FTIR spectroscopy, XRD
and N2 adsorption. Detection, qualitative analysis and
identification of organic impurities in the TiO2 gel and
also the determination of the degree of their removal in the
course of pyrolysis were carried out by TGA methods in
combination with the gas chromatographic analysis and
mass spectrometry.
Titanium isopropoxide was diluted with isopropyl alco-
hol in a flow of nitrogen; then, a carboxylic acid (formic or
oxalic) was added with vigorous stirring, which was fol-
lowed by dropwise addition of hydrochloric acid, which
R0
R1
Xerogel
R10
Xerogel
400 8C+
700 8C600 8C
400 8C+
400 8C+ +
Xerogel
600 8C
600 8C+
700 8C
+ +700 8C
+
+
is anatase, is brookite, is rutile.
Figure 9. Fig. 9. Scheme of phase transformations in samples R0, R1
and R10 (see text) for different calcination temperatures.61
The content of individual phases is roughly proportional to the surface
of the corresponding circle.
3
1
2
100 300 500 T /8C0
10
20
30
40
50
TiO
2particlesize
/nm
Figure 10. Average particle size of TiO2 in R0 (1), R1 (2) and R10 (3)
samples (see text) at different calcination temperatures.61
6 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
served as the hydrolysis catalyst. This produced an emulsion
that transformed into a uniform gel in 4 days.
The molar ratio Ti(OPri)4 : carboxylic acid : isopropyl
alcohol : water : HCl= 1 : 1 : 20 : 1 : 0.0184 was found to be
optimum.62, 63 However, the physicochemical characteristics
of TiO2 samples synthesized in the presence of formic and
oxalic acids 63, 64 substantially differed.
Thus according to N2 adsorption isotherms, a mesopo-
rous material was formed in the presence of HCOOH that
was characterized by specific surface of 480 m2 g71 and the
average pore diameter of 2.7 nm.62 IR Spectroscopic studies
showed that the sample contained Ti7O7Ti fragments,
formate groups coordinated with titanium and non-hydro-
lyzed titanium isopropoxide. Absorption bands belonging
to organic impurities in the TiO2 gel completely disap-
peared upon heating the samples above 340 8C. According
to data from XRD, the gel represented an amorphous
product that crystallized at temperatures above 400 8C to
form the anatase phase.
According to the data on N2 adsorption, the sample
formed in the presence of (COOH)2 represented a macro-
porous material with specific surface of 18 m2 g71 and the
average pore diameter of 24.4 nm.63 IR Spectroscopic
studies showed that titanium dioxide samples contained
oxalate groups coordinated with titanium and also non-
hydrolysed titanium isopropoxide. Absorption bands of
organic impurities in the TiO2 gel completely disappeared
in samples heated above 550 8C. According to data from
XRD, the original gel also represented an amorphous
product (cf. Ref. 62), but the anatase crystallization
occurred at temperatures above 550 8C.As was shown by different physicochemical methods
(XRD, IR spectroscopy, TGA, electron spectroscopy of
diffuse reflectance (ESDR), ammonia thermoprogrammed
desorption (TPD), adsorption methods),64 the introduction
of the sulfate ions into TiO2 decreased the particle size,
stabilized the anatase phase and increased both the specific
surface and the pore volume (Table 1). The dependences of
all parameters on the amount of sulfuric acid added in the
impregnation had extrema. The sol ± gel hydrolysis product
of titanium isopropoxide in the presence of nitric acid was
employed for the impregnation. After ageing, the sol
formed was concentrated, dried, impregnated with sulfuric
acid (0.5 mol litre71, 2 ± 10 ml) and calcined.
Among modified methods for the preparation of nano-
sized TiO2, mention should be made of hydrolysis and
condensation of titanium isopropoxide in anhydrous etha-
nol using a cellophane membrane that makes it possible to
control the diffusion rate.65 Hydrolysis combined with
sonication is advantageous controlling the size of titanium
dioxide nanoparticles.66
TiO2 Nanoparticles of different shapes (spherical, cubic
and hexagonal rods) and sizes (50 ± 500 nm) were prepared
from titanium butoxide as the precursor.67 Hydrolysis of
Ti(OBun)4 was carried out in the presence of different
surfactant compositions and concentrations. The prepared
TiO2 nanoparticles were studied for photocatalytic decom-
position of Methyl Orange in fixed film batch reactors. It
was shown that the shape is more important than the size:
TiO2 nanorods had higher photocatalytic activities than
spherical and cubic TiO2 nanoparticles.
The dependence of the morphology, the size and the
crystal structure of nano-sized crystalline titanium dioxide
on the hydrolysis conditions of titanium butoxide was
studied in detail.68 Hydrolysis of Ti(OBun)4 was carried
out at room temperature in inverse micellar systems formed
by an aqueous solution of a mineral acid, cyclohexane and a
surfactant Igepal1 CO-520 [4-(n-C9H19)C6H4O(CH2CH2.
.O)4CH2CH2OH]. The effect of the following hydrolysis
conditions, such as concentration (c) and type of acid
(hydrochloric, nitric, sulfuric or phosphoric), molar content
of water [w=H2O : surfactant and h=H2O : Ti(OBun)4],
and hydrolysis time (t) on the formation, crystal phase,
morphology, and size of the TiO2 particles were investi-
gated.
It was shown that the pH of the reaction medium had a
significant effect on the crystal structure of the obtained
TiO2 nanoparticles. For example, according to TEM data,
an amorphous product was formed when the hydrochloric
acid concentration was below 2 mol litre71, all other con-
ditions being equal. At the HCl concentration of 2 mol
litre71, the resulting TiO2 particles represented a mixture of
anatase and rutile. The pure rutile phase was formed as the
acid concentration reached 2.5 mol litre71. At still higher
HCl concentration (to 4 mol litre71), the amorphous TiO2
was formed again.
In the case of HCl at c=2.5 mol litre71, h=28,
t=20 days and w=3, finely disperse shuttle-like TiO2
nanoparticles with widths 35 ± 40 nm and lengths
150 ± 160 nm with the crystalline structure of rutile were
formed. As the parameter w increased from 3 to 5, both the
widths and the lengths of the particles increased slightly
without changes in their morphology. For w=10, the
particles formed petal-shaped aggregates with retention of
their crystalline structure. It is believed that the aqueous
cores of inverse micelles served as microreactors for the
hydrolysis of titanium butoxide. With the increase in
parameter w, the number of these micelles increased, they
had to coalesce; and thus, shuttle-like rutile nanoparticles
from different micelles formed petal-like aggregates with the
same crystal phase. However, the anatase phase appeared in
aggregates for w=12, probably because micelles were
destroyed in the course of reaction with such a high water
content.
For c=2.5 mol litre71, w=8, t=20 days, the effect of
parameter h was similar to the aforementioned effect of
parameter w. For h<6, i.e., below the coordination num-
ber of Ti(IV) ions, the amount of water in micelle cores was
insufficient for the complete hydrolysis of titanium butox-
ide. It this case, the crystallization slowed down and
amorphous TiO2 was formed. For h>10, the amorphous
product transformed into crystalline rutile. For h=10 ± 20,
the nanoparticle size remained virtually unchanged; how-
Table 1. Adsorption characteristics of sulfated TiO2 .64
Samp- Specific Pore Particle Rutile Porele a surface volume size /nm content diameter
/m2 g71 /cm3 g71 (%) /�A
T 35 0.09 12.71 46.6 103.4
ST2 91 0.21 9.62 0 95.0
ST4 98 0.18 8.62 0 74.1
ST6 79 0.12 7.48 0 58.1
ST8 57 0.11 11.05 0 78.4
ST10 48 0.10 11.74 18.3 85.5
a The following designations were used: T is the original TiO2;
ST2 ± ST10 are samples prepared by impregnation with 2, 4, 6, 8 and
10 ml, respectively, of sulfuric acid (0.5 mol litre71).
Synthesis and stabilization of nano-sized titanium dioxide 7
ever, for h=36, flower-shaped aggregates were formed.
High h values accelerated the butoxide hydrolysis and the
crystalline TiO2 particles formed were capable of aggrega-
tion both inside the aqueous cores of micelles and also in
their environment.
As the hydrolysis time increased from 5 to 10 and
20 days all other conditions remaining standard (see
above), the growth of particles with subsequent aggregation
and morphological changes (Fig. 11) was observed.
Hydrochloric, nitric, sulfuric and phosphoric acids used
to adjust the pH of the medium were employed to examine
the effect of the nature of acids.68 The parameters w and h
were taken to be 8 and 28, respectively, and the acid
concentration was equivalent to 2.5 M HCl, all other things
being the same. The nature of acid was found to substan-
tially affect the crystalline phase composition, morphology
and also the size of TiO2 nanoparticles. Thus substitution
of nitric acid for hydrochloric acid decreased the width of
shuttle-like particles to 20 ± 25 nm and their length to
*120 nm. The use of sulfuric or phosphoric acids irrespec-
tively of their concentration resulted in the formation of
amorphous rather than crystalline spherical TiO2, namely,
uniform small spheres with diameter of *40 nm for sulfuric
acid and coarse spheres with diameter of *240 nm for
phosphoric acid (Fig. 12). Presumably, this can be associ-
ated with different affinity of the anions with respect to
Ti(IV) ions in aqueous solutions (Cl7 and NOÿ3 exhibited
weak affinity, while SO2ÿ4 demonstrated strong affinity).
The strong affinity of SO2ÿ4 for titanium inhibits the
titanium dioxide rearrangement and, hence, the overall
crystallization process. It thus follows 68 that phosphoric
acid, like sulfuric acid, is the crystallization inhibitor.
Acetic acid often used in the hydrolysis of titanium-
containing precursors can also serve as an efficient stabilizer
of the anatase phase in the calcination. Thus the hydrolysis
of an acetic-acid solution of Ti(OPri)4 with aqueous ammo-
nia at pH 3 ± 4 and 70 8C afforded a gel that showed an
400 nm
400 nm
400 nm
a
c
b
Figure 11. TEM microimages of TiO2 particles formed upon hydrol-
ysis of Ti(OBun)4 under standard conditions for 5 (a), 10 (b) and
20 days (c).68
400 nm
400 nm
400 nm
a
c
b
Figure 12. TEM microimages of TiO2 particles formed upon hydrol-
ysis of Ti(OBun)4 in the presence of different mineral acids.68
(a) Nitric acid, (b) sulfuric acid, (c) phosphoric acid.
8 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
anatase phase even at 1000 8C.69 However, as the hydrolysis
medium pH increased to 5, pure rutile was formed at
1000 8C, whereas at pH 6, anatase to rutile transformation
is complete at 800 8C (Table 2), as for samples prepared by
hydrolysis in the absence of acetic acid.
Monodisperse non-aggregated nanoparticles of titanium
dioxide were prepared 70 by hydrolysis of titanium butoxide
at 60 8C in the presence of acetylacetone and p-toluenesul-
fonic acid. It was shown that a thorough choice of synthesis
conditions that rule out gelation makes it possible to
produce particles with the anatase structure and the average
size of 1 ± 5 nm. It was found 70 that the optimum conditions
for synthesizing nanodisperse TiO2 sols are as follows: the
initial molar ratio (a) acetylacetone : metal 14 a4 6; the
molar ratio h=H2O : Ti 54 h4 10 and the acidity of the
medium expressed through the molar ratio h+=H+ : Ti,
04 h+4 0.8. In the mentioned variation ranges of param-
eters a, h and h+, the titanium concentration in the sol
could change from 0.5 to 1 mol litre71. Drying of a nano-
disperse sol to form a xerosol could be accomplished by
centrifugation, evaporation of solvent in vacuum at room
temperature or by heating at 100 8C.The prepared xerosol could be dispersed again without
aggregation in a water ± ethanol or ethanol solution. This
afforded sufficiency concentrated sols (>1 mol litre71 with
respect to titanium) containing TiO2 particles with the size
of 1 ± 5 nm, the same as in the original sol.70 This was
proved by the data from TEM and quasi-elastic light
scattering. The use of other physicochemical research meth-
ods (XRD, IR spectroscopy, 13C, 17O and 1H NMR, mass
spectrometry, etc.) in studying TiO2 nanoparticles has
shown that particles were protected from aggregation by
complexes with acetylacetone formed on their surface,
which agreed with other results,52 and also by a mixed
organic-inorganic adsorption layer formed from acetylace-
tone, p-toluenesulfonic acid and water.
Nanodisperse (particle size 3.8 nm) pure anatase with
the specific surface of 359.1 m2 g71 was prepared based on
the same precursor, i.e., titanium butoxide.71
IV. Nano-sized TiO2 synthesis based on TiCl4 ;product dispersion and phase composition
Titanium tetrachloride belongs to the most widely used
titanium dioxide precursors; it was employed in both the
synthesis of substrates and catalysts by the precipitation
method 72, 73 and preparation of nano-sized TiO2 colloid
solutions by the sol ± gel method.
Thus a colloid solution of TiO2 nanoparticles
(40 ± 60 �A), was prepared 74, 75 in an inert medium by drop-
wise addition of a TiCl4 solution to cold water (pH
3.5 ± 4.0). The temperature and the reactant mixing rate
were regulated by an apparatus designed for automatic
preparation of colloid systems.76 The TiO2 concentration
(0.1 ± 0.6 mol litre71) was determined from the concentra-
tion of the peroxide complex after dissolving the colloid in
concentrated sulfuric acid by a known procedure. 77 The
possibility of preparation of surface complexes of titanium
dioxide colloid nanoparticles with cysteine to be used in
photocatalysis was demonstrated.74, 75
Titanium dioxide was also synthesized 78 by thermal
hydrolysis of TiCl4 in a propanol ± water mixture. The
dependence of the precipitate morphology on the propa-
nol : water volume ratio, the TiCl4 concentration, temper-
ature and the presence of a dispersant, namely,
hydroxylpropylcellulose (HPC), was studied. It was shown
that titanium dioxide prepared in a 3:1 (by volume) prop-
anol : water mixture contained uniform-dispersed spherical
particles. With the addition of HPC, the nanoparticle size
distribution became narrower. The spherical shape of TiO2
particles was independent of the TiCl4 concentration, but
their sizes increased with an increase in the suspension
concentration. An increase in the synthesis temperature
favoured the broader size distributions of particles. The
effect of the liquid-phase temperature gradient on the
morphology of TiO2 particles was also noted. The mor-
phology and size of titanium dioxide particles were studied
by SEM and TEM methods; phase transitions were inves-
tigated by the XRD method.
In another study,79 titanium dioxide was synthesized by
the hydrolysis of TiCl4 in a strongly acidic aqueous solution
in the absence and in the presence of poly(ethylene glycol)
PEG-1000 that served as the dispersant for controlling the
shape and size of the TiO2 particles. It was shown that in
the absence of PEG-1000, uniform shuttle-shaped TiO2
nanocrystals were formed and the degree of their aggrega-
tion increased with an increase in the acid content and a
decrease in the TiCl4 concentration. In the presence of
PEG-1000, TiO2 particles with sufficiently narrow size
distributions were prepared, with the particle diameter
decreasing with an increase in the PEG-1000 amount. The
process was characterized by simplicity and a low cost and
could be carried out in a continuous mode. The products
were studied by the XRD and TEM methods.
In yet another study,80 titanium dioxide sols were
prepared by acid hydrolysis of TiCl4 (pH of the medium
was adjusted by addition of an ammonia solution), followed
by peptization of precipitates with nitric acid. Stable titania
sol (particle size 14 nm) was prepared at the molar ratio
H+ : Ti=0.5 with vigorous stirring for 1 day at 70 8C(Table 3). It is remarkable that the activity of TiO2 in
photocatalytic reactions was largely determined by the
degree of dispersion of TiO2 rather than by the promoting
effect of modifying additives (0.5% Pt or 10% of Si, Zr, W,
Mo oxides) introduced into TiO2 to increase its activity.
Nanosized TiO2 powders prepared by controlled
hydrolysis of TiCl4 in aqueous solutions in the presence of
small amounts of sulfate ions were studied 81 by TEM, high-
resolution EM, XRD and electron diffraction; the specific
surface was determined from adsorption isotherms using the
Brunauer ± Emmett ± Teller (BET) equation. It was shown
that the hydrolysis of TiCl4 at 70 8C carried out in the
presence of the sulfate ions produced a powder that con-
Table 2. Phase composition a of calcined TiO2 samples as a function of thepH of acetic acid-containing solution of titanium isopropoxide during thehydrolysis.69
Calcination Hydrolysis medium pHtemperature /8C
3 4 5 6
1000 A+R A+R R R
800 A+R (traces) A+R (traces) A+R R
600 A A A A
400 A A A A
aUsed designations: A is anatase, R is rutile.
Synthesis and stabilization of nano-sized titanium dioxide 9
sisted of the pure anatase phase with the predominant
particle size of 3.5 nm, which is much smaller than in
powders prepared from titanium alkoxides. Moreover, the
anatase ± rutile phase transformation retarded. However, at
the same hydrolysis temperature but in the absence of the
sulfate ions, the product represented a mixture of anatase
and rutile, the primary particle size in the rutile phase was
4.3 nm. Hydrolysis at 20 8C led to TiO2 powders with the
amorphous structure and high specific surfaces
(*500 m2 g71). According to the electron spectroscopic
data, the presence of the sulfate ions accelerated the anatase
phase formation.
According to the literature data, from the practical
viewpoint, TiO2 in the form of anatase is often preferred
to rutile. Optical and electrochemical properties of anatase
and the third modification of titanium dioxide, i.e., broo-
kite, were compared and the conditions of synthesis of each
phase by the sol ± gel method were described.82 It was
demonstrated that the formation of one or another phase
was determined by not only the pH of the solution, but also
the molar ratio Cl : Ti , which was controlled in the interval
17 ± 35 by the addition of NaCl. In addition, the simulta-
neously formed brookite and rutile phases were character-
ized by different degrees of dispersion and could easily be
separated.
Studies by XRD and Raman spectroscopy 83 revealed
traces of brookite in anatase in nano-sized TiO2 samples
prepared by precipitation from TiCl4 at different pH. The
average size of TiO2 crystals after 2-h treatment at 450 8Cwas 7 ± 9 nm. The lattice parameter c of anatase increased as
the pH of the medium increased during the synthesis, while
the volume fraction of the brookite phase increased with a
decrease in pH. It was shown that the temperature range of
anatase transformation to rutile shifted to low temperatures
as the brookite volume fraction increased, i.e., the brookite
phase was to a certain extent responsible for the anatase
transformation to rutile.
A simple method of synthesis of high purity brookite
nanoparticles was described.84 Hydrolysis of TiCl4 was
carried out in acidified isopropyl alcohol at ambient tem-
perature and the peptization and crystallization of the gel
formed occurred on refluxing. The data from SEM and
TEM revealed the formation of spherical TiO2 with the
average size of 30 nm. The data from XRD confirmed the
presence of the brookite crystalline structure. The degree of
particle agglomeration could be predicted based on the
amount of heat released during the hydrolysis of TiCl4 .
Ultradisperse TiO2 samples with the structures of ana-
tase, rutile and their mixture assayed for the photocatalytic
degradation of phenol were synthesized 85, 86 by hydrolysis
of TiCl4 . The resulting product was studied by high
resolution EM, XRD, BET and electron spectroscopy. In
the catalytic process mentioned, the highest selectivity (very
low concentrations of side products, namely, p-benzoqui-
none and hydroquinone) was observed for catalyst particles
in the anatase phase measuring 4 nm, whereas rutile par-
ticles of the same size exhibited selectivity that differed
insignificantly from that of coarse-grain rutile. Presumably,
calcination was effective in increasing the activity of the
TiO2 catalyst because this favoured perfection of its crystal
structure.
The addition of (NH4)2SO4 and adjustment of the pH to
7 (with NH4OH) resulted in anatase in the final stage; in the
absence of ammonium sulfate, a mixture of anatase and
rutile was formed. To prepare rutile, the same process was
carried out without both ammonium sulfate and ammo-
nium hydroxide. In each case, the hydrolysis product
represented titanium dioxide hydrate (TiO2. nH2O), which
was centrifuged off, dried and, if necessary, calcined.
Nanodisperse titanium dioxide was fabricated 87 by
CO2-laser-assisted pyrolysis of TiCl4 in a gas ± vapour
mixture. The effect of synthesis conditions, namely, the
laser power and the oxidant (air) delivery rate, on the
structural characteristics of synthesized TiO2 was studied.
It was shown that moderate acceleration of the air delivery
increased the degree of crystallinity, the grain size, and the
rutile content.
V. Synthesis of TiO2 based of miscellaneoustitanium-containing precursors
Besides alkoxides and TiCl4, yet another TiO2 precursor
used in the preparation of anatase nanocrystals, namely,
ammonium dihydroxodilactatotitanate(IV) (ALT), deserves
mention.88 According to the available published data, this
compound attracted attention as the starting material in the
preparation of catalysts,89 fabrication of electrodes for
medicinal purposes 90 and production of UV-radiation-
proof films on different surfaces.91 In contrast to titanium
alkoxides that are rapidly hydrolyzed, ALT is stable in
neutral solutions at ambient temperatures and decomposes
to form TiO2 (anatase), NH3 and sodium lactate only above
100 8C or in aqueous NaOH solutions. However, even
under these conditions, ALT hydrolysizes more slowly;
this makes it possible to synthesize nanocrystalline TiO2
with predominantly oblate-shaped particles and a narrow
size distribution; the latter is especially important for the
synthesis of TiO2 films.
Studies on ALT thermohydrolysis (up to 300 8C in
hermetically sealed glass tubes or in a titanium autoclave
has shown 88 that the size of formed anatase nanoparticles
increased with the increase in the hydrolysis temperature
(Fig. 13) and ALT concentration. Thus, it can be regulated
by varying these parameters. In all the cases, extremely
narrow particle size distributions were obtained. With the
addition of ammonium lactate to the reaction mixture, the
effects of ALT concentration and the reaction time on the
size of TiO2 particles became negligibly small, and the
growth of particles stopped. This simple trick can be used
for the interruption of the process to afford high yields of
virtually uniform size anatase nanocrystals. The final prod-
uct contains no admixtures (ions Cl7, Na+).
Nanocrystalline TiO2 was prepared 92 using an uncon-
ventional method, namely, plasma synthesis from a tita-
nium hydride TiH2 powder.
Table 3. TiO2 sol particle size at different concentrations of HNO3
(TiO2 concentration 0.3125 mol litre71).80
H+ :Ti (mol.) Particle size /nm Sol stability
0.08 precipitate was not
peptized
0.2 102 stable
0.4 45
0.5 14
0.7 56
1.0 96
1.2 7 unstable
10 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
VI. Stabilization of the disperse state and phasecomposition of nano-sized TiO2 sols
Despite the efficacy of using the sol ± gel method for the
synthesis of nanocrystalline TiO2 sols, the pronounced
trend of TiO2 particles to aggregation during both the
hydrolysis of a titanium-containing precursor and long-
term storage of sols still remains the main problem of this
method; aggregation is often accompanied by variations in
the phase composition. The analysis of published data
allowed the ways for solving this problem to be outlined.
Thus an acidic medium (pH=1.8) and a low storage
temperature (4 8C) favoured higher stability of TiO2 colloid
solutions.22 Moreover, the stability of non-aqueous sols
tended to increase under low humidity conditions.53 The
nature of solvent also affected the size and the stability of
TiO2 colloid particles.52 On the whole, the majority of
studies stressed that strict observance of the synthesis
conditions (pH, temperature, precursor concentration) and
also of the stoichiometric ratio of the reactants and the
addition order is very important for the targeted synthesis
of TiO2 with desired properties.53, 59, 68 ± 70
Stable nanodisperse TiO2 sols can be prepared if organic
disaggregating and stabilizing additives, namely, acetylace-
tone,52, 70 diethanolamine,53 polyacrylic acid,59 methylcellu-
lose,57 hydroxypropylcellulose,78 poly(ethylene glycol),79
etc., are introduced into the reaction mixture. Disaggregat-
ing additives operate through different mechanisms,
namely, the inhibition of hydrolysis and condensation,52, 53
which favoured the lower degree of aggregation of particles;
the formation of surface organic-inorganic complexes with
TiO2 nanoparticles, which prevented aggregation;52, 70 the
shift of balance of attractive and repulsive forces as a result
of which the sedimentation rate decreased.57
One of the most popullar methods of sol stabilization
was the peptization of the hydrolysis product (after its
centrifugation and rinsing with water) with nitric acid on
vigorous stirring. The peptized precipitate was again centri-
fuged and dispersed in water.80, 82
In certain practical applications of nano-sized TiO2, the
stabilization of its phase composition was of no less impor-
tance than the definite size of nanoparticles. The amor-
phous TiO2 phase was as a rule formed upon hydrolysis at
20 8C.45, 81 The sol ± gel method not only provided a possi-
bility for regulation and reproduction of the ratio of TiO2
crystal phases (anatase, rutile and brookite) in the final
product, but also allowed preparation of each phase in its
pure form. Like the control over the grain size of TiO2, this
was achieved 70 by accurate choice of the conditions of
hydrolysis of titanium-containing precursors (pH, temper-
ature, time, ratio of main components).22, 68, 81, 82, 85, 93, 94
Certain specific conditions for the formation of different
TiO2 phase compositions were mentioned. For example, the
hydrolysis of TiCl4 (Ref. 81) or titanium isopropoxide 64 in
the presence of a small amount of the sulfate ions favoured
the formation of the individual anatase phase, whereas in
the absence of the sulfate ions, a mixture of anatase and
rutile was formed under the same conditions.64, 81 However,
it was shown 68 that the strong affinity of SO2ÿ4 ions for
titanium suppressed rearrangement of titanium dioxide and,
hence, the overall crystallization process.
From the viewpoint of synthesizing pure anatase, it was
of interest to use titanyl sulfate as the precursor. The
substitution of an aqueous solution of TiOSO4 (0.25 mol
litre71) for the amorphous TiO2. nH2O gel in the hydro-
thermal synthesis of nano-sized TiO2 decreased the temper-
ature of anatase formation from 250 to 150 8C, all otherconditions being the same.95 According to Table 4, this
afforded highly disperse anatase with the particle size that
increased with the increase in the temperature of hydro-
thermal treatment to 250 8C but nonetheless remained
smaller than in anatase synthesized from amorphous TiO2
gel. With the increase in the TiOSO4 solution concentration
to 0.44 mol litre 71, the anatase particle size increased and
the use of a TiOSO4 solution in sulfuric acid (0.25 mol
litre71) led to the appearance of the rutile phase at 250 8C.This is consistent with the data of Ref. 64 (see Table 1).
The synthesis of pure and stable nano-sized anatase was
described 49, 50 (hydrothermal and solvothermal syntheses).
Acetic acid added in the stage of hydrolysis strictly at
pH 3 ± 4 served as an efficient agent for stabilizing the
anatase phase up to 1000 8C (see Table 2).69
As was mentioned above, non-standard titanium-con-
taining precursors and synthesis conditions were sometimes
used in the preparation of pure anatase and for controlling
the quantitative ratio of anatase, rutile and broo-
kite.60, 65, 66, 88, 92
4
8
12
16
0120 160 200 240 T /8C
TiO
2particlesize
/nm
Figure 13. Dependence of the average TiO2 particle size on the hydrol-
ysis temperature.88
ALT Concentration in water is 0.415 mol litre71, duration of process
is 24 h.
Table 4. Grain size of nanocrystalline anatase prepared by hydrothermalsynthesis from an amorphous TiO2
. nH2O gel and an aqueous TiOSO4
solution.95
Precursor Concent- Synthesis Particle Specificration conditions size a /nm surface a
/mol litre71 /m2 g71
T /8C time XRD TEM
Gel 250 10 min 27 35 60
TiO2. nH2O 250 6 x 28 38 7
TiOSO4 0.25 250 10 min 16 20 7in water 250 6 h 18 24 7
150 10 min 10 8 7150 6 h 14 16 7
0.44 250 6 h 20 28 98
TiOSO4 0.25 250 10 min 24 26 7in 1M H2SO4 250 6 h see b 22 7
a These parameters were determined with the accuracy of �10%.b In this case, a mixture of anatase (85%) and rutile (15%) was formed;
the particle size was 20 nm for anatase and 30 nm for rutile.
Synthesis and stabilization of nano-sized titanium dioxide 11
* * *
The material of the present review clearly demonstrated that
the problem of synthesizing stable forms of nano-sized
titanium dioxide is being successfully solved. Materials
with desired structural and morphological characteristics
were fabricated using either conventional methods by scru-
pulous selecting synthesis conditions or by new approaches
(new reactants, unusual methods of treatment of the reac-
tion mixtures, improved instrumental implementation). It
can be assumed that the directions of further studies in this
field will be determined by the requirements imposed by
practical application of nano-sized TiO2 , first of all, in
medicine. The first positive results in this field will undoubt-
edly attract attention of scientists and engineers and the
quest for new applications of nano-sized TiO2 will pose new
problems for synthetic chemists.
This review was prepared with financial support by the
Russian Foundation for Basic Research (Project No. 08-04-
01045-a), the Siberian Branch of the Russian Academy of
Sciences (Integration Project No. 61), Programmes of the
Ministry for Education and Science of the Russian Feder-
ation `Development of the Scientific Potential of the Higher
School' (Project No. 2.1.1/5642).
References
1. D T Ros, G Spalluto, A S Boutorine, R V Bensasson, M Prato
Curr. Pharm. Des. 7 1781 (2001)
2. D G Knorre, V V Vlasov, V F Zarytova, A V Lebedev,
O S Fedorova Design and Targeted Reactions of Oligonucleotide
Derivatives (Boca Raton, FL: CRC Press, 1994)
3. D T Ros, G Spalluto, M Prato, T Saison-Behmoaras,
A S Boutorine, B Cacciari Curr. Med. Chem. 12 71 (2005)
4. M Ferrary Curr. Opin. Chem. Biol. 9 343 (2005)
5. R Beutner, J Michael, A FoÈ rster, B Schwenzer, D Scharnweber
Biomaterials 30 2774 (2009)
6. T Paunesku, T Rajh, G Wiederrecht, J Maser, S Vogt,
N Stojicevic, M Protic, B Lai, J Oryhon, M Thurnauer,
G Woloschak Nat. Mater. 2 343 (2003)
7. T Matsunaga, R Tomoda, T Nakajima, H Wake FEMS
Microbiol. Lett. 29 211 (1985)
8. B Kim, D Kim, D Cho, S Cho Chemosphere 52 277 (2003)
9. N Suketa, T Sawase, H Kitaura, M Naito, K Baba, K Nakayama,
A Wennerberg, M Atsuta Clin. Implant Dent. Relat. Res. 7 105
(2005)
10. Y Lan, C Hu, X Hu, J Qu Appl. Catal., B: Environ. 73 354 (2007)
11. L Zan, W Fa, T Peng, Z-K Gong J. Photochem. Photobiol., B 86
165 (2007)
12. A-G Rinco n, C Pulgarin Appl. Catal., B: Environ. 49 99 (2004)
13. M F Dadjour, C Ogino, S Matsumura, N Shimizu Biochem.
Eng. J. 25 243 (2005)
14. P Hajkova, P Spatenka, J Horsky, I Horska, A Kolouch Plasma
Process. Polym. 4 S397 (2007)
15. US P. 0071790 (2003)
16. US P. 02640 (2007)
17. Ch GoÈ bbert, inHandbook for Clearing/Decontamination
of Surfaces (Eds I Johansson, P Somasundaran)
(Amsterdam: Elsevier, 2007) p. 813
18. Y Zhao, S Sugiyama, T Miller, X Miao Exp. Rev. Med. Devices 5
395 (2008)
19. A Fujishima, R Cai, J Otsuki, K Hashimoto, K Itoh,
T Yamashita, Y Kubota Electrochim. Acta 38 153 (1993)
20. A Mills, S Hunte J. Photochem. Photobiol., A 108 1 (1997)
21. A Fujishima, T Rao, D Tryk J. Photochem. Photobiol., C 1 1
(2000)
22. A P Zhang, Y P SunWorld J. Gastroenterol. 10 3191 (2004)
23. V F Zarytova, A S Levina, M N Repkova, A S Ivanyi,
Z R Ismagilov, N V Shikina, V V Zinovjev, E F Belanov,
E G Malygin, S N Zagrebelnyi, S I Baiborodin, inMaterials
of the 6th International Conference `High Medical Technologies
in XXI Century', Benidorm, Spain, 2007 p. 73
24. N V Shikina, Z R Ismagilov, F V Tuzikov, L T Tsikoza,
V F Zarytova, V V Zinoviev, S N Zagrebelnyi, in Tezisy
Dokladov Vserossiiskoi Konferentsii s Mezhdunarodnym
Uchastiem `KATEK-2007', Sankt-Peterburg, 2007 (Abstracts
of Reports of the All-Russian Conference with International
Participation `KATEK-2007', St Petersburg, 2007) p. 302
25. V Zinoviev, A Evdokimov, E Belanov, E Malygin, S Balachnin,
O Serova, D Pletnev, V Zarytova, A Levina, M Repkova,
Z Ismagilov, N Shikina, S Zagrebelnyi, S Baiborodin Antiviral
Res. 78 A51 (2008)
26. V F Zarytova, A S Levina, M N Repkova, A S Pavlova,
V V Zinov'ev, A A Evdokimov, E F Belanov, S M Balakhnin,
E G Malygin, Z R Ismagilov, N V Shikina, S I Baiborodin,
S N Zagrebelnyi, inMaterialy IV S'ezda Rossiiskogo
Obshchestva Biokhimikov i Molekulyarnykh Biologov,
Novosibirsk, 2008 (Proceedings of IVth Congress of Russian
Society of Biochemists and Molecular Biologists, Novosibirsk,
2008) p. 315
27. V F Zarytova, V V Zinoviev, Z R Ismagilov, A S Levina,
M N Repkova, N V Shikina, A A Evdokimov, E F Belanov,
S M Balakhnin, O A Serova, S I Baiborodin, E G Malygin,
S N Zagrebelnyi Allergologiya i Immunologiya 8 235 (2007)
28. J M Veranth, E G Kaser, M M Veranth, M Koch, G S Yost
Part. Fibre Toxicol. 4 (2) 1 (2007)
29. T Moritz, J Reiss, K Diesner, D Su, A Chemseddine J. Phys.
Chem. B 101 8052 (1997)
30. Y Wang, M Wu, W F Zhang Electrochim. Acta 53 7863 (2008)
31. M R Hoffman, S T Martin, W Choi, D W Bahnemann
Chem. Rev. 95 69 (1995)
32. B Liu, L Wen, X Zhao Sol. Energy Mater. Sol. Cells 92 1358
(2008)
33. J-MGiraudon, T BNguyen, G Leclercq, S Siffert, J-F Lamonier,
A AboukaõÈ s, A Vantomme, B-L Su Catal. Today 137 379 (2008)
34. A Dey, S De, A De, S K De Nanotechnology 15 1277 (2004)
35. S W Oh, S H Park, Y K Sun J. Power Sources 161 1314 (2006)
36. H Zhou, L Liu, K Yin, S L Liu, G X Li Electrochem. Commun.
8 1168 (2006)
37. R Wang, KHashimoto, A Fujishima Nature (London) 388 431
(1997)
38. Y Qiao, S-J Bao, C M Li, X-Q Cui, Z-S Lu, J Guo ACSNano 2
113 (2008)
39. D M AntonellyMicroporous Mesoporous Mater. 30 315 (1999)
40. L Malfatti, P Falcaro, H Amenitsch, S Caramori, R Argazzi,
C A Bignozzi, S Enzo, M Maggini, P InnocenziMicroporous
Mesoporous Mater. 88 304 (2006)
41. L T Tsykoza, N A Kulikovskaya, N K Zhulanov,
Z R Ismagilov React. Kinet. Catal. Lett. 60 323 (1997)
42. Z R Ismagilov, L T Tsikoza, R A Shkrabina, V A Sazonov,
N V Shikina Kinet. Katal. 39 607 (1998) a
43. Z R Ismagilov, R A Shkrabina, S A Yashnik, N V Shikina,
I P Andrievskaya, S R Khairulin, V A Ushakov, J A Moulijn,
I V Babich Catal. Today 69 351 (2001)
44. J Le, Z Zhou, H Wang, G Li, Y WuDesalination 212 123 (2007)
45. V A Dzis'ko, A P Karnaukhov, D V Tarasova,
in Fiziko-khimicheskie Osnovy Sinteza Okisnykh Katalizatorov
(Physicochemistry Foundations of the Synthesis of Oxide
Catalysts) (Novosibirsk: Nauka, 1978) p. 46
46. M R Harris, G Whitaker J. Appl. Chem. 13 348 (1963)
47. V M Chertov, N T Okopnaya, I E Neimark Dokl. Akad. Nauk
SSSR 209 876 (1973) b
48. H Cheng, J Ma, Z Zhao, L Qi Chem. Mater. 7 663 (1995)
49. A L Castro, M R Nunes, A P Carvalho, F M Costa,
M H Floreà ncio Solid State Sci. 10 602 (2008)
12 Z R Ismagilov, L T Tsykoza, N V Shikina, V F Zarytova, V V Zinoviev (deceased), S N Zagrebelnyi
50. R K Wahi, Y Liu, J C Falkner, V L Colvin J. Colloid Interface
Sci. 302 530 (2006)
51. R C Asher, S J Gregg J. Chem. Soc. 5057 (1960)
52. H-J Chen, L Wang, W-Y ChiuMater. Chem. Phys. 101 12 (2007)
53. A Verma, S A Agnihotry Electrochim. Acta 52 2701 (2007)
54. J Beusen, M K Van Bael, H Van den Rut, J D'Haen,
J Mullens J. Eur. Ceram. Soc. 27 4529 (2007)
55. S Mahshid, M Askari, M S Ghamsari J. Mater. Process.
Technol. 189 296 (2007)
56. A Fernandez, A Caballero, A R Gonzalez-Elipe, J-M Herrmann,
H Dexpert, F Villain J. Phys. Chem. 99 3303 (1995)
57. M H Habibi, M Nasr-Esfahani Dyes Pigm. 75 714 (2007)
58. C A Martinez-Perez, P E Garcia-Casillas, H Camacho-Montes,
H A Monreal-Romero, A Martinez-Villafane, J Chacon-Nava
J. Alloys Compd. 434 ± 435 820 (2007)
59. H-J Chen, P-C Jian, J-H Chen, W Leeyih, W-Y Chiu Ceram. Int.
33 643 (2007)
60. D H Kim, H W Ryu, J H Moon, J Kim J. Power Sources 163 196
(2006)
61. J Yu, J C Yu, W Ho,M K-P Leung, B Cheng, G Zhang, X Zhao
Appl. Catal., A: General 255 309 (2003)
62. R Campostrini, M Ischia, L Palmisano J. Therm. Anal.
Calorim. 71 997 (2003)
63. R Campostrini, M Ischia, L Palmisano J. Therm. Anal.
Calorim. 71 1011 (2003)
64. K R Sunajadevi, S SugunanReact. Kinet. Catal. Lett. 82 11 (2004)
65. N Wetchakun, S Phanichphant Curr. Appl. Phys. 8 343 (2008)
66. D Neppolian, Q Wang, H Jung, H Choi Ultrason. Sonochem. 15
649 (2008)
67. D Liao, B Liao Int. J. Chem. Reactor Eng. 5 A24 (2007)
68. D Zhang, L Qi, J Ma, H Cheng J. Mater. Chem. 12 3677 (2002)
69. C Suresh, V Biju, P Mukundan, K G K Warrier Polyhedron 17
3131 (1998)
70. E Scolan, C Sanchez Chem. Mater. 10 3217 (1998)
71. L Mao, Q Li, H Dang, Zh ZhangMater. Res. Bull. 40 201 (2005)
72. I P Olen'kova, G A Zenkovets, D V Tarasova,
I A Ovsyannikova Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Neorg.
Mater. 13 383 (1977)
73. V Yu Gavrilov, G A Zenkovets Kinet. Katal. 31 168 (1990) a
74. T Rajh, A E Ostafin, O I Micic, D M Tiede, M C Thurnauer
J. Phys. Chem. 100 4538 (1996)
75. T Rajh, O Poluektov, A A Dubinski, G Wiederrecht,
M C Thurnauer, A D Trifunac Chem. Phys. Lett. 344 31 (2001)
76. M C Thurnauer, L M Tiede, T Rajh Acta Chem. Scand. 51 610
(1997)
77. R C Thompson Inorg. Chem. 23 1794 (1984)
78. C-S Fang, Y-W ChenMater. Chem. Phys. 78 739 (2003)
79. R Chu, J Yan, S Lian, Y Wang, F Yan, D Chen Solid State
Commun. 130 789 (2004)
80. Y Zhang, G Xiong, N Yao, W Yang, X Fu Catal. Today 68 89
(2001)
81. Q Zhang, L Gao, J Guo J. Eur. Ceram. Soc. 20 2153 (2000)
82. M Koelsch, S Cassaignon, J F Guillemoles, J P Jolivet
Thin Solid Films 403 ± 404 312 (2002)
83. Y Hu, H-L Tsai, C-L Huang J. Eur. Ceram. Soc. 23 691 (2003)
84. B I Lee, X Wang, R Bhave, M HuMater. Lett. 60 1179 (2006)
85. Q Zhang, L Gao, J Guo Appl. Catal., B: Environ. 26 207 (2000)
86. Q Zhang, L Gao, J Guo Nanostruct. Mater. 11 1293 (1999)
87. M Scarisoreanu, M R Alexandrescu, R Birjega, I Voicu,
E Popovici, I Soare, L Gavrila-Florescu, O Cretu, G Prodan,
V Ciupina, E Figgemeier Appl. Surf. Sci. 253 7908 (2007)
88. H MoÈ ckel, M Giersig, F Willig J. Mater. Chem. 9 3051 (1999)
89. A Hanprasopwattana, T Rieker, A G Sault, A K Datye
Catal. Lett. 45 165 (1997)
90. US P. 4692273 (1987)
91. S Baskaran, L Song, J Liu, Y I Chen, G L Graff J. Am. Ceram.
Soc. 81 401 (1998)
92. P V A Padmanabhan, K P Sreekumar, T K Thiyagarajan,
R U Satpute, K Bhanumurthy, P Sengupta, G K Dey,
K G K Warrier Vacuum 80 1252 (2006)
93. S Qiu, S J Kalita Mater. Sci. Eng., A 435 ± 436 327 (2006)
94. N Venkatachalam, M Palanichamy, V MurugesanMater.
Chem. Phys. 104 454 (2007)
95. Yu VKolen'ko, A A Burukhin, B B Churagulov, N NOleynikov
Mater. Lett. 57 1124 (2003)
a Ð Kinet. Catal. (Engl. Transl.)b Ð Dokl. Chem. (Engl. Transl.)
Synthesis and stabilization of nano-sized titanium dioxide 13